The present disclosure relates to an image reading apparatus and an image forming apparatus.
Conventionally, an image reading apparatus that reads an original document to generate image data is known, and for example, the image reading apparatus is fitted to an image forming apparatus such as a copying machine. The image reading apparatus described above includes, for example, a light source, an image sensor and an A/D conversion portion.
The light source generates light that is applied to the original document of a target to be read. The image sensor receives light reflected off the original document, and outputs an analog signal corresponding to the amount of the reflected light that has been received. The A/D conversion portion converts the analog output of the image sensor from analog to digital to output digital image data.
Here, for example, when the analog output of the image sensor exceeds the upper limit value of the input voltage range (convertible range) of the A/D conversion portion, even if the analog output of the image sensor is varied such that the analog output of the image sensor is increased, a digital value after the A/D conversion is not varied, and all the analog output is converted into the maximum digital value. When as described above, the output of the A/D conversion portion is saturated, for example, if a bright image is included in the original document of the target to be read, all the bright image is read as white, with the result that a phenomenon called white skipping occurs (the image quality is degraded).
Hence, normally, light amount adjustment on the light source is performed so that the maximum value of the analog output of the image sensor (for example, the analog output of the image sensor reading a white reference plate for shading correction) is prevented from excessing the upper limit value of the input voltage range of the A/D conversion portion.
Conventionally, when power is input to the image reading apparatus, as an initial adjustment, not only a light amount adjustment but also a gain adjustment, an offset adjustment and the like are performed. Thus, since after the input of power to the image reading apparatus, with various setting values such as a light amount setting value set at the optimum values, it is possible to perform a job, the degradation of the image quality is reduced. However, when the initial adjustment including the light amount adjustment is performed, a waiting time since the input of power to the image reading apparatus until it is possible to perform the execution of the job is made long Hence, this is inconvenient for a user.